1. Field of the Invention
The present invention relates to a short circuit detection circuit and a control method, and particularly to a short circuit detection circuit and a control method that can be applied for detecting short circuit of a series of light-emitting diodes.
2. Description of the Prior Art
In an energy saving and carbon reduction era, a light-emitting diode can be used for a popular light source due to higher luminous efficiency and an smaller component size of the light-emitting diode. For example, liquid crystal panel manufacturers are gradually utilizing light-emitting diode light sources as a substitute for traditional cold-cathode fluorescent lamp light sources as backlight sources of liquid crystal panels.
FIG. 1 is a diagram illustrating a light-emitting diode power supply 8 applied as a backlight module of a liquid crystal panel. The light-emitting diode power supply 8 is mainly used for controlling turning-on of a plurality of series of light-emitting diodes L1-LN, where each series of light-emitting diodes of the plurality of series of light-emitting diodes L1-LN has a plurality of light-emitting diodes. In a booster 4, a pulse width controller 23 can control a power switch to make an inductor component sink power from an input terminal IN and release power to an output terminal OUT. Thus, the booster 4 can build a proper output voltage VOUT at the output terminal OUT to drive the plurality of series of light-emitting diodes L1-LN. A current balance controller 13 controls current flowing through each series of light-emitting diodes to be the same to make luminance of each series of light-emitting diodes the same.
A circuit 12 has a plurality of diodes all coupled to a minimum voltage terminal MIN for detecting a minimum voltage of cathode terminals D1-DN. A voltage VMIN of the minimum voltage terminal MIN roughly corresponds to the minimum voltage of the cathode terminals D1-DN. In addition, the current balance controller 13 can also influence transmission efficiency of the burst circuit 4 through a control terminal CTRL to make the voltage VMIN maintain a predetermined voltage value. Thus, NMOS transistors N1-NN can be ensured to operate in a more efficient state to reduce unnecessary power consumption.
Some light-emitting diodes of the plurality of series of light-emitting diodes L1-LN may be aging, short circuit, or open circuit with increase in using time. When the plurality of series of light-emitting diodes L1-LN have abnormal operational states, the current balance controller 13 should execute a corresponding operation to prevent the plurality of series of light-emitting diodes L1-LN from being damaged.
A circuit 14 can provide short-circuit detection. The circuit 14 has a plurality of diodes all coupled to a maximum voltage terminal MAX. A voltage VMAX of the maximum voltage terminal MAX roughly corresponds to the maximum voltage of cathode terminals D1-DN. For example, if the series of light-emitting diodes Ln has a plurality of light-emitting diodes that are short circuited, a cathode voltage VDn of a cathode terminal Dn is much higher than other cathode voltages VD1-VDn-1 when the plurality of series of light-emitting diodes L1-LN are turned on, resulting in the voltage VMAX of the maximum voltage terminal MAX being increased. The current balance controller 13 can detect the voltage VMAX through a detection terminal SD. Therefore, when the voltage VMAX exceeds a threshold value, the current balance controller 13 can determine that a light-emitting diode short circuit event occurs, and further turn off the plurality of series of light-emitting diodes L1-LN.
However, the light-emitting diode power supply 8 in FIG. 1 has disadvantages as follows:
First, the current balance controller 13 can not determine which one of the plurality of series of light-emitting diodes L1-LN has a light-emitting diode short circuit event. That is to say, the current balance controller 13 still turns off all series of light-emitting diodes when only one series of light-emitting diodes Ln has a light-emitting diode short circuit event. Second, cost of the light-emitting diode power supply 8 is very expensive. The light-emitting diode power supply 8 needs a high voltage switch coupled between the maximum voltage terminal MAX and the detection terminal SD to prevent high cathode voltages VD1-VDN from being inputted to the current balance controller 13 when the plurality of series of light-emitting diodes L1-LN are turned off (dimming off). Thus, the current balance controller 13 needs an additional pin DT to control the high voltage switch.